Polyuronic acids

Methods of analysis. The polyuronic acid content (PUAC) and the degree of esterification (DE) were determined according to Owens et al (10). 

Abbreviations PUAC, polyuronic acid content DE, concentration ri, specific viscosity Mj, molecular mass... 

J. C. Gonzalez, S. I. Garcia, S. Bellu, A. Atria, J. M. Salas-Peregrin, A. Rockenbauer, L. Korecz, S. Signorella, and L. F. Sala, Oligo and polyuronic acid interactions with hypervalent chromium, Polyhedron, 28 (2009) 2719-2729. 

In conclusion, the remarkable influence on DAP activity exerted by the low-viscosity PGA vehicles is an issue deserving further attention, in view of the possible implication of a muco-adhesive mechanism. A closer study of the potential interactive properties of polyuronic acids and of their drug salts with the precorneal mucin might lead to a better understanding of the bioadhesive properties of these and other similar anionic polymeric materials, and of their influence on ocular drug bioavailability. 

The hemicelluloses also include the polyuronides, or polyuronic acids, for instance a polymer of a hexuronic acid such as galacturonic acid. There is a possible generic link between the polyuronides and the pentosans since the latter might be produced as the result of the decarboxylation of hexuronic acids. The possibility of transforming hexuronic acids into pentosans by the removal of carbon dioxide... 

The use of nitrogen dioxide for the selective oxidation of polysaccharides to polyuronic acids was introduced by Kenyon and his coworkers13,63 in 1941. By this means extensive oxidation of the primary alcohol groups in cellulose was obtained, through the mechanism of preferential nitration followed by decomposition of the nitric acid ester with carboxyl forma-tion.68(0< > Apparently some undissociated nitration products also were formed, since infrared absorption studies54 indicated the presence of nitrate radicals in the polyuronic acid. Side reactions produced carboxyl,... 

Microbial mats and biofilms, defined as surface layers of microbes entrained in a matrix of extracellular polymeric substances (EPS) (Characklis and Marshall, 1989), are also important in changing the surface texture and erodibility of sediments in estuaries (de Beer and Kiihl, 2001). The EPS are primarily composed of cellular-derived polysaccharides, polyuronic acids, proteins, nucleic acids, and lipids (Decho and Lopez, 1993 Schmidt and Ahring, 1994). The EPS can serve as a cementing agent for surface sediment particles, thereby affecting the erodibility of sediments as well as the flux of dissolved constituents across the sediment-water interface (de Beer and Kiihl, 2001). 

Plant gums, which occur as exudates on the bark or leaves of trees, are salts of polyuronic acids and are usually freely soluble in water. It is often difficult to decide whether such polysaccharides are homogeneous, but a beginning has now been made in the determination of their structures. Weak linkages have been shown to be present, and it is possible to remove portions of the molecules that are readily hydrolyzable by mild acid, leaving a more stable acidic residue. The structure of the gums appears to depend upon the source, and some studies are complicated by the fact that the botanical origin of the gum was not known with certainty. 

Although little is known about the effects of pectins on the absorption of manganese, administration of pectin has been shown to increase the excretion of bile acids in humans (48). In the only previous study related to the influence of pectin on manganese metabolism, fuccidan—a polyuronic acid of seaweed origin—was found to reduce the uptake of manganese in tied-off segments of rat jejunum by up to 77% (51). 

In the separation of oligosaccharides, sulfonic acids (mono-, di- or tri-) of aminonaphthalene have been used [29]. Polyuronic acids hke hyaluronic acid have also been characterized by CE [30]. 

Arabans and galactans are generally much less abundant than the polyuronic acids and, in contrast to these, are neutral. Arabans are branched out polymers of L-arabofuranose residues. They are constituted of a linear chain where residues are a(1 5) glycosidically linked L-arabofuranose residues are a(l->3) alternately bound as lateral chains of single units. 

The knowledge of only the primary structure of complex carbohydrates is no longer sufficient to understand and explain their function and specificity [61]. The three-dimensional structures of pectin and polyuronic acid determine their interactions with other ions, molecules and macromolecules and are significant for their function and biological activity [88,102-103] Computational chemistry methods may greatly help in the determination of the three-dimensional structure of polysaccharides allowing to xmderstand and explain the behaviour of the PGA chains and the diffusion of ions inside. We apphed [89-92] Molecular Dynamics (MD) to the study of the motion of small (6-24 units) Polygalacturonic Acid (PGA) chains either protonated or complexed by Na" and Ca ions. 

Alginic acid is a polyuronic acid composed of residues of D-mannuronic acid and L-guluronic acid and is obtained chiefly from algae belonging to the Phaeo-phyceae, mainly species of Laminaria. 

Studies of the methylation products have also supplied evidence for the identification of these acids. After complete methylation and hydrolysis of the aldobionic or polyuronic acid, it is often possible to isolate the methylated uronide as the lactone, or methyl ester. The acid may also be oxidized to the methylated dibasic acid and identified as such. Furthermore, after methylation and hydrolysis of pectic and... 

Humic acids are those humic substances that are precipitated at pH = 1. Fulvic acids stay in solution at pH = 1 they contain more —COOH and —OH groups than humic acids. Dissolved organic acids, which are not retained by a nonionic XAD resin, are hydrophilic acids, they are not very well defined They contain, in addition to single aliphatic acids, uronic and polyuronic acids. 

The PhEur 2005 describes alginic acid as a mixture of polyuronic acids [(CgHgOeU composed of residues of D-mannuronic and L-glucuronic acid, and is obtained mainly from algae belonging to the Phaeophyceae. A small proportion of the carboxyl groups may be neutralized. 

In order to understand the binding of cations by polyuronic acids, like pectin, Grant (27) refers to three main factors that must be considered ... 

It is important to note that under the anaerobic conditions existing in the sapropel negligible amounts of humic acids are present. The humic acids that do exist account for less than 5% of the organic matter and are structurally unrelated to the humin. They are essentially polyuronic acids and are only called humic acids because they are operationally extracted as such (Hatcher et al., 1983b). Thus, it is unlikely that humic acids are intermediates in the formation of humin in this environment. Selective preservation is the simplest explanation for the existence of humin. 

Fulvic acids. Marine sedimentary humic substances soluble in base and acid (fulvic acids) have previously been examined by and NMR (12). The dominant structural components were postulated to be polysaccharide - like substances, probably polyuronic acids. Solid-state NMR spectra of fulvic acids isolated from a number of marine and estuarine sediments are shown in Figure 1. Major peaks at 72 and 106 ppm betray the overwhelming presence of polysaccharide -like substances, and, as shown by Hatcher and others (12.), the moderate peak for carboxyl or amide carbon at 175 ppm suggests that these polysaccharides are more like polyuronides. Aromatic carbons (110 to 160 ppm) are decidedly minor components. Aliphatic carbons (0-50 ppm) are also minor components. H NMR spectra shown by Hatcher and others (12) indicate that these aliphatic structures are highly branched. 

Although most polysaccharide lyases and epimerases act on the polyuronic acids, a number of those acting on pectin do so on the methyl esters. Whereas the second pifa of acetic acid is around 35-36, the of ethyl acetate is 25, ... 

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